Field of the Invention
The present invention relates to a hydrocracking process of heavy hydrocarbon distillates using a supercritical solvent, and, more particularly, to a hydrocracking process for converting low value-added heavy hydrocarbon distillates into high value-added hydrocarbon distillates using a supercritical solvent as a medium.
Description of the Related Art
Recently, demands for transport oils, particularly, light oil products, have continuously increased, whereas demands for heavy oil products, such as bunker oil and the like, have decreased. However, the ratio of high-sulfur crude oil and heavy crude oil to produced crude oils has gradually increased compared to in the past. Moreover, according to concerns about petroleum resource exhaustion, it has been continuously required to develop technologies for upgrading low-priced heavy hydrocarbon distillates, such as heavy distillates obtained during a crude oil refining process, bitumen (an alternative to crude oil) and the like, to produce high value-added light oil products and petrochemical raw material distillates.
As a typical example of such low-grade heavy distillates, there is a vacuum residue which is an oil distillate recovered from the bottom of a reduced-pressure distillation tower during a crude oil refining process (e.g., the vacuum residue is obtained at a pressure of 25 to 100 mmHg, and has a boiling point of about 813.15 K or more at atmospheric pressure). Because such low-grade heavy distillates have low H/C ratios and high viscosity, they are difficult to upgrade. Further, typically, heavy distillates, particularly, a vacuum residue, have high contents of sulfur, nitrogen, oxygen and heavy metals (e.g., vanadium, nickel, iron and the like) as well as polyaromatic compounds, such as asphaltene and the like.
In relation to this, various methods of upgrading heavy hydrocarbon distillates have been proposed. One of these methods includes a process for converting low value-added heavy hydrocarbon distillates having a high boiling point into high value-added hydrocarbon distillates having a low boiling point.
Conventional examples of the above-mentioned converting process include, for example, cracking, hydrocracking, catalytic cracking, steam cracking and the like. However, this converting process generally requires extreme operation conditions of high temperature, high hydrogen pressure and the like, and uses a hydrogenation catalyst having a weak acidic support to prevent the formation of coke. In relation to this, a vacuum residue is known to have hydrocracking characteristics different from those of light oil.
Meanwhile, recently, processes of treating and upgrading crude oil or heavy distillates in a supercritical medium or solvent have been developed. For example, Korean Unexamined Patent Application Publication No. 2010-0107459 describes a process for recovering an oil distillate having a low content of asphaltene, sulfur, nitrogen or a metal as well as having a low heavy component content by bringing heavy distillates stream into contact with supercritical water to convert the heavy distillates into refined heavy distillates; Japanese Unexamined Patent Application Publication No. 2008-297468 describes a process for decomposing heavy distillates under the supercritical condition of a saturated hydrocarbon solvent (e.g., dodecane, normal hexane, cyclohexane and the like); and U.S. Pat. No. 4,559,127 describes a process for converting a high-boiling hydrocarbon distillate, such as a vacuum residue, into a low-boiling hydrocarbon distillate using halogen or hydrogen halide as a catalyst under the supercritical condition of an acidic aqueous solution medium.
Most commonly-known processes are processes of converting heavy hydrocarbon distillates into low-boiling hydrocarbon distillates using water or a saturated hydrocarbon solvent as a supercritical medium in the presence of a catalyst. In this case, as typical examples of high value-added oil distillates that can be obtained from an upgrading process, there are naphtha (IBP to 177° C.) and a middle distillate (177 to 343° C.). Particularly, a middle distillate has been attracting considerable attention recently, in accordance with the increase in demands for aviation oil and diesel oil (light oil), because it includes kerosene and diesel oil in an oil refining process. However, when a conventional supercritical solvent is used, the conversion of a low value-added oil distillate into a high value-added distillate (particularly, a middle distillate as a raw material of diesel oil) is insufficient, requiring improvement of the conventional supercritical solvent to prevent the formation of coke.
Moreover, the conventional technology is disadvantageous in that the composition of the converted oil distillate is greatly changed depending on hydrogen pressure. For this reason, there is a problem in that a reaction of converting heavy distillates into high value-added oil distillates, such as a middle distillate (and/or naphtha), must be conducted under relatively high partial pressure of hydrogen.
Therefore, it is required to develop a hydrocracking process for heavy hydrocarbon distillates using a supercritical solvent, which can reduce the formation of coke even under the condition of low hydrogen pressure compared to that of a conventional technology, which can maintain a high conversion ratio and which can improve the selectivity of a middle distillate, the demand for which has recently increased.